PR
Meaning of PR: Its presence usually means the estrogen pathway is working, since estrogen signaling is what switches this receptor on.
Definition of PR
PR is the abbreviation for progesterone receptor, a protein inside certain cells that binds the hormone progesterone and, once bound, alters which genes the cell reads. It is found in the lining of the uterus, in breast tissue and in some tumors. The same two letters mean other things in clinical notes, including per rectum and the PR interval.
What does the receptor do normally?
Progesterone rises after ovulation and acts through this receptor to prepare the lining of the uterus to receive an embryo and then to maintain a pregnancy, holding the muscle of the uterus quiet. In the breast it drives development of the milk-producing structures. Like the estrogen receptor it sits inside the cell and works by binding DNA and altering the reading of nearby genes, so its effects unfold over hours and involve many proteins rather than one. Two forms of the progesterone receptor exist, produced from the same gene, and they can have different effects within the same tissue.
Why is it tested alongside the estrogen receptor?
The gene that makes the progesterone receptor is itself switched on by estrogen signaling. That single fact explains most of how the result is read: finding the receptor is evidence that the estrogen pathway in those cells is intact and functioning, not merely that the estrogen receptor protein is present. A tumor positive for both receptors responds to endocrine treatment more reliably than one positive for the estrogen receptor alone, and losing the progesterone receptor while keeping the other is taken as a sign that the pathway has been disrupted. This is why the two appear together on every hormone receptor report in breast cancer, alongside HER2.
What else do the letters PR mean?
| Context | Meaning |
|---|---|
| Pathology report | Progesterone receptor |
| Prescription or examination note | Per rectum, meaning by or via the rectum |
| Observation chart | Pulse rate |
| Electrocardiogram | The PR interval, the time from atrial to ventricular activation |
| Cancer treatment response | Partial response |
Nothing distinguishes these except where the abbreviation appears, which is a general hazard of two-letter abbreviations in clinical records and a reason many services now write the words out.
Also known as
Used in a sentence
The pathology report listed the tumor as PR positive following receptor testing on the biopsy sample.
Good to know
PR status is typically reported alongside estrogen receptor status, since the two receptors are related but distinct and a tumor can be positive for one, both or neither.